A major unsolved problem of developmental biology is the molecular basis for the localization of egg cytoplasmic determinants that appear to control differential gene expression in the early embryo. We plan to investigate the genetics and molecular biology of cytoplasmic localization in the free living soil nematode C. elegans, an organism that is becoming an increasingly important model system for development. Our long-range goals are to understand the molecular nature of cytoplasmic determinants, the mechanism by which they control subsequent gene expression. During the initial project period we shall try to 1. obtain additional evidence for cytoplasmic localization in C. elegans embryos, 2. develop assays for partitioning of developmental potential and specific macromolecules in early cleavages, 3. identify lethal maternal-effect mutants in which abnormal partitioning leads to blocks in early embryogenesis, and 4. investigate these mutants for clues to the nature, localization mechanism, and function of the cytoplasmic determinants. In addition, we shall attempt to learn more about macromolecular synthesis during oogenesis and early embryogenesis, to demonstrate somatic crossing over as a method for producing genetic mosaics, and to find conditions for maintenance and if possible growth of embryonic cells in tissue culture.